She's her traditional summoner self. She summons Ixion, Valefor, Shiva, and Bahamut so far in confirmation but I'm pretty sure it will be all of her summons from X. Her EX-Burst is The Sending.
This has not been confirmed. It's speculated because of the trialers cause he's mistaken by some of the other heroes of cosmos for being a possible hero of light. It seems this might be a part of the story but Kuja has not been officially stated as a Warrior of Cosmos. The scene in question makes it seem like no one knows for sure in the game and it's a simple problem
No word, the event seems more about XIII-2 and KH3DS. It's possible that's all we'll get but it's also very likely they are still waiting to reveal a few more people.
Like Kuja, this is speculation. The evidence used to support this theory is his absence from the box cover for the Limited Edition Duodecim Soundtrack but it's not like Prishe is on the box either. Chances are he's either a warrior of cosmos who got snubbed from the artwork or he's not affiliated with either side, or perhaps he's the mystery Light Warrior that Kuja is mistaken for. Who knows, once again SE has been mum about it but I feel it's too early to say for sure he's on one side or the other.
EDITGA: Here's a really crappy quality version of the trailer from the event. It shows Yuna (if you can tell... from the terrible video quality) fighting, as well as Prishe, Aerith being used as an assist, Tidus' new shirtless outfit, and the tiny hint of Gilgamesh. Watch it before Squenix finds it and has it pulled from youtube like the Versus trailer was.
This image also popped up somewhere... WoL's third alt outfit perhaps?
Also the director said his team was going to add all the characters possible... possible DLC or is there more to Duodecim than SE is letting on?
W-EDITGA: Replaced crappy trailer with better one.